Lake Lisan and the Dead Sea: Their Level Changes and the Geomorphology of their Terraces

Changes in the level of closed lakes such as the glacial Lake Lisan/Near East, that occupied the Jordan Rift Valley between 80 to 15 ka BP, reflect climatic changes in evaporation and precipitation patterns. However, in an actively subsiding basin such as the Dead Sea (water level today is at -423 m relative to mean sea level), tectonic activity could also contribute to lake level recession. The retreat of Lake Lisan left behind a sequence of shoreline terraces and deposits of aragonite and gypsum. The ability to determine shore line elevations and to date them offers an excellent possibility to evaluate hydrologic changes, paleoclimatic conditions and tectonic activity of the lake basin during the Last Glacial. By the end of the Pleistocene, Lake Lisan receded sharply and was followed by the current Dead Sea at ~10 ka BP. Both lakes experienced several rises and regressions due to climatic change. However, the most recent lowering of the Dead Sea level since the beginning of the twentieth century of more than 30 m is mainly due to the impact of upstream freshwater diversion together with mineral extraction by the salt industry in the southern Dead Sea basin. This recent level drop left behind a unique landscape of shore line terraces, allowing investigation of the recent lake regression in detail. Therefore the dissertation aims at (1) examining the most recent changes in the Dead Sea level and shore morphology and developing a terrain model of the Dead Sea Rift Valley that allows calculating the area and volume losses of the lake for the various stages of its recession. (2) investigating geomorphological characteristics of Lake Lisan erosional terraces along the eastern side of the Dead Sea (e.g., elevation, gradient, width, length, etc.) and dating them. This investigation will help to reconstruct the lake level history and correlate the level changes with paleoclimatic conditions. Moreover, it should give additional water level data and rates of level retreat for Lake Lisan; and (3) investigating geochemical and mineralogical characteristics of the terrace stromatolites (AAS and XRD) and analyzing their stable isotope composition. This should provide indicators on the lake levels and on the lake water chemistry as well as on paleoenvironmental and paleoclimatic conditions. The main results of this study are as follow: (1) Well-correlated and dated profiles of the modern shoreline terraces of the Dead Sea are presented for the first time. The timing and amplitude of the lake level change recorded in these terraces forms an analogue to past level changes of the paleo-Dead Sea and even to level changes of other lakes. (2) A terrain model of the Dead Sea Rift Valley was developed based on SRTM data that served as a tool to calculate the volume and area functions versus altitude of the Dead Sea. The model was further used in macro-engineering implications to calculate the water input requirements of the rapidly shrinking Dead Sea and therefore the capacity of the projected Dead Sea-Red Sea Canal. The water volume loss calculated by this study (0.47 km³/a) and the ground water inflow to the Dead Sea (ca. 0.5 km³/a) suggest that the RSDS should has a capacity of ~1 km³/a in order to stop the lake level drop. However, ca. 1.3 km³/a is required in order to fill the lake back to levels as of 30 years ago. (3) The morphological and chronological evidence presented in this study allowed generating a high resolution curve of the lake level for MIS 2 (32-10 ka BP). It can now be assumed with certainty that the lake stood as high as -150 m, removing the doubt on the highest stand found along the western coast. However, this is not the highest stand of the lake during MIS 2, much higher terraces up to -137 m were identified in the field and dated between 30 and 32 ka BP. (4) Discovery of high-level terraces of Lake Lisan > -137 m and up to 0 m along the eastern escarpment and dating of their stromatolites revealed the time and the exact elevation of the highest lake stand. This also clarified the previous doubt on the paleoenvironment conditions of the early stage of Lake Lisan as well as on the transition period from Lake Samra to Lake Lisan. The newly discovered maximal level is 150 m higher than previously reconstructed and occurred at the beginning of the last glacial period (79-76 ka BP). This allowed presenting a new curve of the lake level during the last glacial period, including new fixes on past lake level elevations as well as on the chronology of the regression and transgression cycles. (5) The new curve allows correlating the lake level with global climatic records: transgressions occurred during the warm MIS 5 and 3, while regressions occurred during the cold MIS 4, 2, and the cold Heinrich events 6, 5, 4, 3 and 2. This demonstrates a strong linkage between the paleoclimate of the Jordan valley and monsoon-affected North Africa rather than that with Europe and the North Atlantic. X-ray analysis, Mg/Ca ratios and isotope analyses of the stromatolites correlate well with transgression-regression phases of the lake. Dominance of calcite in stromatolites at -76 to 0 m and low isotope values in addition to inferred low Mg/Ca ratios of the lake water (i.e. ~2) imply a high fresh water input of the lake during the period of the highest stands. A high Mg/Ca ratio of the lake water of > 7 inferred from stromatolites at -350 m and the existence of aragonite as the sole mineral in this sample reflect low fresh water input and high evaporation rates of the lake during its regression to this low level. Low Mg/Ca ratios and low stable isotope values of stromatolites at -247 to -101 m in addition to the existence of calcite as a main mineral phase indicate wet climatic conditions that caused a lake transgression during MIS 3. The appearance of more aragonite in stromatolites at -137 to -154 m inferring a change to high Mg/Ca ratios and high stable isotope values points to a return to dry climatic conditions that caused a regression of Lake Lisan during MIS 2 between 32 and 22 ka BP